1. Field of the Invention
This invention relates to gelled liquid hydrocarbon fluids and methods of their use and preparation.
2. Description of the Prior Art
High viscosity gelled hydrocarbon liquids have heretofore been utilized in treating subterranean formations penetrated by well bores, e.g., hydraulic fracturing stimulation treatments. In such treatments, a high viscosity gelled liquid hydrocarbon fracturing fluid having particulate proppant material, e.g., sand, suspended therein is pumped through a well bore into a subterranean formation to be stimulated at a rate and pressure such that one or more fractures are formed and extended in the formation. The suspended proppant material is deposited in the fractures when the gelled hydrocarbon fracturing fluid is broken and returned to the surface. The proppant material functions to prevent the formed fractures from closing whereby conductive channels remain through which produced fluids can readily flow to the well bore.
Polyvalent metal salts of orthophosphoric acid esters have heretofore been utilized as gelling agents for forming high viscosity gelled liquid hydrocarbon fracturing fluids. Such gelled liquid hydrocarbon fracturing fluids have included fracture proppant material and delayed breakers for causing the fracturing fluids to break into relatively thin fluids whereby the proppant material is deposited in formed fractures and the fracturing fluid is produced back. Descriptions of such heretofore utilized high viscosity gelled liquid hydrocarbon fracturing fluids and methods of their use are set forth in U.S. Pat. No. 4,622,155 issued to Harris et al. on Nov. 11, 1986, and U.S. Pat. No. 5,846,915 issued to Smith et al. on Dec. 8, 1998. The gelled liquid hydrocarbon fracturing fluids described in the above patents utilize ferric iron or aluminum polyvalent metal salts of phosphoric acid esters as gelling agents and delayed breakers such as hard burned magnesium oxide which is slowly soluble in water.
While the heretofore utilized high viscosity gelled liquid hydrocarbon fracturing fluids and methods have been used successfully for forming fractures in subterranean formations, problems have been encountered as a result of the use of the gelling agent, i.e., the polyvalent metal salt of a phosphoric acid ester. That is, in recent years plugging of refinery towers which process oil produced from formations fractured with gelled liquid hydrocarbon fracturing fluids has caused many expensive, unplanned shut-downs. The plugging material is high in phosphorus and has been attributed to the phosphate esters used as gelling agents. The phosphate esters contribute volatile phosphorus which condenses on distillation tower trays, causing plugging. The volatile phosphorus may also carry over the tops of the distillation towers causing contamination of the hydrocarbon products produced.
Thus, there are needs for improved methods of using and preparing gelled liquid hydrocarbons which upon breaking and being refined substantially reduce volatile phosphorus in distillation towers, improved liquid hydrocarbon gelling agents and improved gelled liquid hydrocarbon compositions. More specifically, in fracturing oil producing subterranean formations in areas where volatile phosphorus is a problem in refineries, there is a need to reduce the production of volatile phosphorus in the refineries to levels where the above described unscheduled refinery shut downs are not required without compromising CO2 compatibility with the gelled oil fracturing fluids used. Concentrations of CO2 as high as 40-50% are commonly used in gelled oil fracturing fluids which form miscible mixtures with the fluids. The presence of the CO2 enhances fluid recovery, minimizes the amount of oil based fracturing fluid which must be recovered, and reduces costs in areas where CO2 is less expensive than the oil based fracturing fluid.